With the development of modern, more complex aerodynamic power generation machines, there has been an increased amount of study into the inspection of machine components to develop methods of inspecting such components for defects in non-invasive ways. Some of the most critical components of the machines are in locations that allow limited access to them. Most studies to date have used visual, radiographic, liquid penetrant and eddy current non-destructive methods of inspection. To perform visual, liquid penetrant and eddy current tests, it is necessary to have access to all surfaces of the machine component being tested. For many machine components, this is not possible without at least some disassembly of the machine.
To perform a radiographic exam, a piece of radiographic film must be placed on the opposite side of the machine component being examined using the radiation source. There must also be a minimal amount of material between the radiation source and the component being tested. In a fully assembled machine, it is often not possible to accomplish either of these tasks.
Traditionally, the use of ultrasound to test machine airfoils for defects has been limited due to the thin and complex geometries of airfoils in general. The largest problem with using ultrasound to test airfoils is that the surfaces of an airfoil from which a test can be done constantly changes in angle with respect to the area of interest in the airfoil. To perform an inspection of a changing surface using ultrasound, the use of many discrete transducers at a variety of angles would be required. As such, the use of a single transducer would be impractical and unreliable.
U.S. Pat. No. 6,082,198, discloses the use of phased array ultrasound to inspect for defects from a surface which is at a constant angle to the area to be inspected. The disclosed method inspects from the hub, and relies on a constant access of symmetry. It cannot be used with parts which are contained in a machine due to the need for access to a beam entry surface that is blocked by other components.
Airfoils are a highly stressed component of aerodynamic machines. Because of these high stresses, an airfoil should be inspected regularly for defects. To perform non-destructive tests on airfoils, the machines which contain these parts must be disassembled to some extent to gain access to the entire airfoil. This disassembly is costly and time-consuming. To reduce the time and cost involved with the disassembling of a machine, a non-destructive technique is needed which will not be affected by a continual change in geometry over the entire airfoil surface.